In the battle for fans and audience members, today’s multipurpose arenas are boasting bigger and better scoreboards, over-the-top amenities, and unique and varied seating options to lure spectators out of their homes (and off of their smartphones) and into the arenas to watch the games, competitions, and concerts.

Arenas, as opposed to larger stadium venues, have the nimbleness to support the quick and varied changeovers required by the variety of events and attractions utilizing the spaces. However, to optimally support current and future venue needs, these arenas must have the ability to adapt and upgrade.

Photo courtesy of Thornton Tomasetti

With its flexibility, adaptability, high strength-to-weight ratio, and ability to support long spans, structural steel—like that used for Barclays Center in Brooklyn—is a material of choice for today’s multipurpose arenas.

One key aspect of this equation is the roof design. “The roof often comprises the largest surface area on an arena, and the vast, unobstructed program space it shelters below offers maximum flexibility for reconfiguration and reuse,” states John Cerone, principal, SHoP Architects, New York.

In fact, seating bowls and support spaces are constantly being reinvented to support trending fan behaviors, says Bart Miller, PE, principal, senior project manager, national sports market leader, Walter P. Moore, Houston. Tasked with frequent renovations, it behooves arenas to anticipate future structural support and flexibility needs from the onset.

“Effective planning and informed decision-making early in the design process can save millions in construction costs and generate millions in future revenues,” Miller explains. “Structural steel allows for the most flexibility in structural modifications, as it can be economically configured for optimal column locations and structural framing depths that allow for contiguous open spaces and increased ceiling heights, and it can be easily reinforced or removed in the future if necessary.”

In addition to sporting events, infrastructure must be built to accommodate top music performers and tours.

“Concerts are asking more of arena roof structures with each new tour by applying heavier and more numerous loads, often that move, distributed over much larger areas than ever before,” Miller reports.

High-Capacity Rigging Grids

Consequently, one of the critical design decisions for a long-span roof system is the evaluation of loading assumptions for concert rigging and scoreboards, explains Jeff Callow, PE, LEED AP, principal, Thornton Tomasetti, New York. “No one wants to have tours turn their facility away because they are limited on what they can do and hang from the roof,” he says.

As venues compete for concerts and other events, arenas that have suitable show rigging capacity, frequent and useful points to rig from, and are easy and safe to access are at a great advantage, confirms Brian A. Dickson, PE, SE, senior principal, Magnusson Klemencic Associates, Seattle.

“A clever, experienced arena roof design will integrate the catwalk provisions and rigging points seamlessly into the roof design from the outset,” adds Peter Aryes, global service leader, structural, for Aurecon, an engineering firm active in the Australian and South African market with a specialty in arenas and stadiums.

Putting things into perspective, venues designed as recently as 10–15 years ago can generally support rigging grids of up to 100,000–120,000 pounds concentrated over the center and end stages only. Now those grids are proving inadequate, as today’s heaviest arena shows—such as Kanye West, Drake, and Game of Thrones—can exceed 250,000 pounds with loads distributed widely across the entire venue roof structure.

In response, many venues are now looking to increase their rigging grid capacity and coverage, which often necessitates the addition of rigging beams and may require strengthening of their primary roof structures. “In planning a new facility, owners should consider proportioning their rigging grid to extend across the entire event floor, be configured for optimum speed and accessibility, and provide far more capacity than they think they will need,” recommends Miller. “The construction costs associated with additional capacity and coverage are nominal, making it much wiser to build it now than to retrofit later.”

Image courtesy of AMB Sports & Entertainment

Retractable roofs offer the best of both worlds—an authentic outdoor fan experience and a comfortable, temperature-controlled environment on cold, rainy, or exceptionally hot days—as shown here at Atlanta’s Mercedes-Benz Stadium.

Structural Steel Roofs

In addition to supporting high-capacity rigging loads, structural steel for long-span roof structures is arguably the “right system” for arena and event centers, asserts Dickson.

“Structural steel is familiar and readily available in nearly any market, can accommodate nearly any desired shape, and can span distances of 300 feet to 400 feet with ease,” Miller states.

Additionally, steel structures can be retrofitted by selective structural strengthening of the existing shapes and/or connections to achieve greater capacity.

As a lightweight material with a high strength-to-weight ratio, structural steel supports long spans, which is ideal for fabrication and erection. By manufacturing the members into smaller pieces, they are easier to transport and move onto the job site, where they are then attached. “The versatility of using either bolted or welded connections provides fabricators and erectors with ultimate flexibility in selecting fabrication processes and installation techniques that fit their equipment, capabilities, and often limited project schedules,” Miller explains.

Steel can also be attached to existing concrete structures, or in many cases, columns can be threaded through the existing structure to provide support for new roof elements, adds Cristobal Correa, PE, principal, structures, Buro Happold, New York.

The structural steel members can be easily modified, strengthened, or removed in the field, which is especially important for multipurpose venues with evolving functional, operational, and aesthetic requirements.

Offering some more insight into why steel is particularly suited for large spans with less distance between the columns/supports, Charis J. Gantes, Ph.D., professor of structural engineering, National Technical University of Athens, Greece, explains that as the span increases, the stresses increase proportionally to the square of the span and the deflections proportionally to the fourth power of the span—or in other words, very quickly. It then becomes very difficult to satisfy the stress/strength and deflection/serviceability constraints.

One strategy is increasing the section, but this is not very effective because then the self-weight also increases. Besides adding to cost, this also adds to the weight that the structure must sustain. Gantes explains that in large spans, the structure mostly carries itself, with little reserve left for live loads, and at a certain span length, the structure cannot even carry itself. “Therefore, for large spans, such as in arena roofs, it is effective to use materials that have high allowable stress to satisfy strength constraints and high modulus of elasticity to satisfy serviceability constraints. This makes steel the best and perhaps only choice,” he says.

This issue of minimizing the self-weight of the structure is of primary importance, emphasizes Craig Tracy, vice president, WSP, Montclair, New Jersey, as every pound of self-weight robs capacity from the structure to support external loads, such as snow, wind etc., and each square inch of structure that is added to support self-weight requires more material to support that added weight.

“The inefficiency of this structural tail-chasing is minimized by using materials that have the best strength and stiffness/modulus relative to their density,” Tracy states. “Comparing the best materials available for construction today, one finds that structural steel has a 50 percent higher specific strength and 30 percent higher specific modulus than concrete.”